The present invention relates to a process of pneumatic stirring of a bath of molten metal. More particularly, the present invention relates to stirring of a bath of molten pig iron during refining of the same in a converter by oxygen blown from above onto the bath.
It is known during a refining process of a bath of molten metal by blowing oxygen to the top of the bath to stir the latter by means of a gaseous fluid injected through refractory gas-permeable elements at the bottom of the converter into the bath (French Utility Pat. No. 2,322,202 to IRSID, and Luxembourg Pat. No. 42,419 to CNRM).
The gaseous fluid is usually an inert gas, such as argon or preferably nitrogen, due to the small cost of the latter.
This new technique, which is known in the world as the "LBE process" (Lance-Bubbling-Equilibrium) tends, as its name indicates, to realize an equilibrium between the metal and the slag, thus permitting combining of the respective advantages of the classical refining process by blowing oxygen from the top and by blowing oxygen from the bottom. This technique provides especially a better control of the refining operation, by assuring a greater flexibility as to the choice of the moment, the duration, or to a certain extent the intensity, of the gaseous injection.
This process has, however, certain technological restrictions which limit the possibility to introduce through each element such a large quantity of gas as is desired.
It has therefore already been proposed to replace the stirring gas to be injected by a liquefied gas which vaporizes upon contact with the bath of molten metal. In this way it is possible to obtain, per injection unit, a greater volume of stirring gas than before. (French Pat. No. 2,463,054 to IRSID, corresponding to U.S. Pat. No. 4,340,208.)
Nevertheless, it has been ascertained that, depending upon the type of permeable elements used, the same stand up only more or less to the thermal shocks caused by the repeated injections of cryogenic fluids.